Mapping stable isotopes of oxygen and hydrogen in precipitation, surface waters and groundwaters of Georgia

We present preliminary results of the monitoring of oxygen and hydrogen isotopes in the water cycle of Georgia. The objective of the monitoring is to create maps of isotopic composition of precipitation over Georgia, estimate seasonal amplitudes in the isotopic composition of precipitation, and relationships with the surface and ground waters. Monthly cumulative precipitation samples have been collected since 2013 at 17 sites over entire Georgia at elevations 14 m a. s. l to 2220 m a. s. l. Local meteoric water lines (LMWLs) indicated differences between western, central, and eastern Georgia. Although the LMWLs slopes were mostly not substantially different, only the highest stations (Bakuriani and Gudauri) exhibited slopes that were slightly greater than 8.  The lowest LMWL slope (7.4) was found for stations Chaladidi and Sabueti located in western and central Georgia. LMWL derived for Gudauri (the Greater Caucasus) had a significantly greater intercept (19.9) than at all other sites. Isotopic gradients in delta 18O and delta 2H calculated between stations Tbilisi (430 m a.s.l.) and Gudauri (2220 m a.s.l.) were -0.26 per mil and -1.8 per mil per 100 m, respectively. Monthly samples were collected in several major rivers (Rioni, Mtkvari, Alazani, Iori). Isotopic composition of the greatest Georgian river Mtkvari was best correlated with precipitation in the central Lesser Caucasus (Bakuriani and Sabueti) and southern slopes of the eastern Greater Caucasus (Lagodekhi). One-fourth of groundwater samples were collected in boreholes between mid-July and mid-August and almost all samples from the second half of September (i.e. in the periods without groundwater replenishment) contained evaporated water. Slopes of the evaporation lines were 5.4 and 4.8, respectively.